YouTube is automatically converting at least some videos under 60 seconds to their new Shorts product, which includes a new URL structure (e.g. https://www.youtube.com/shorts/HGgKlO8R0pA) which Composer does not recognize the oembed data from.
Changing the URL from above to the original form/current form for longer videos https://www.youtube.com/watch/?v=/HGgKlO8R0pA is a workaround for now. But it would be nice to support YouTube's new native URL structure.
More on Shorts: https://support.google.com/youtube/answer/10059070?hl=en
Brian McAlister
Thank you for this submission and alerting us to this updated oembed type from YouTube. I've added this to our product backlog for future updating.